My son has a cough and the doctor gave an antibiotic augmentin amoclav 400ml/5mg.. is it OK if it is taken 5ml 3x a day for 10days?

Are you questioning the prescription or the doctor? Is that what is written on the bottle? Wouldn't you be better off asking the doctor instead of the Internet?

It should be taken exactly as prescribed. If you're questioning the dosage contact your doctor.

This antibiotic is a weight based antibiotic. Meaning that the dosage is dependent on your son's weight. You need to follow the dosage exactly as prescribed. If you don't understand, your best course of action would be to call the pharmacy that filled the prescription.